The present invention generally relates to wide band antennas.
In today radiator in antennas such as dipoles, monopoles, Planar Inverted-F antennas (PIFA), log periodic antennas, fractal antennas is formed as a direct or folded electrical line, for example a wire or a printed line. The working frequencies of these antennas depend on a height or a length of their radiators. Therefore, these antennas can operate at certain frequencies only.
All existing antennas are built so as to provide a direction of the currents in the radiator for obtaining specified radiation parameters. This means that the antenna determines, which currents should flow through its radiator. The number of such currents is limited. Therefore, even antennas with a wide frequency range do not work at all frequencies of this band. A log periodical antenna is further known, and it is a wideband antenna. However, the log periodical antenna is not omni directional and it is very bulky.
A dipole and a monopole are known for its superb usage as a linear antenna. However, dipoles and also monopoles cannot be implemented as an internal antenna in devices that include a Printed Circuit Board (PCB).
For example, in cellular handsets and other mobile device, their small PCB, cannot be as a ground plane for needed potential zeroing due to small perimeter [2].
Accordingly, it is an object of the present invention to provide a wideband omni directional antenna which eliminates the above-mentioned disadvantages of the prior art antennas and has only one radiating element. The antenna of the present invention is an omni directional wide band antenna which has a radiator formed as an electrically conductive plate.
The known wide band antennas operate using several separate radiators and thus have several resonance frequencies, so that between these frequencies the parameters of the antennas deteriorate. The wide band antenna of the present invention avoids the disadvantages of the known wide band antennas by operating with needed parameters at all frequencies of a required wide frequency band.
In the antenna according to the present invention the radiator is a plate in which an infinite number of currents can flow. A main part of electric current will flow through the radiator over a distance whose length is equal to an odd number of quarters of the wavelength. As will be seen below, the resistance for such a current is minimal. Therefore, the value of this current will be maximal.
A wide band antenna according to the present invention can have a triangular form. In this case an electric signal can be fed to a lower corner point of the triangle. The two sides of an angle at the lower corner of the triangle have different lengths. A longer side is not shorter than a quarter of the wavelength of the lowest frequency of a predetermined frequency range, while a shorter side is no longer than a quarter of wavelength of the highest frequency of this frequency range. It is desirable that the small side was not a horizontal line.
When a signal is applied, the currents in the radiator can flow in different directions. Each direction is characterized by its resistance. According to the laws of electrical engineering, a maximum current will flow in the direction with a minimal resistance. Such minimal resistance will have a direction with a length equal to a quarter of the wavelength at a given frequency with which the antenna must operate. This resistance (R) is active and equals to an approximately active resistance of monopole with length equals to quarter of a wavelength. If the length of a current path is different from a quarter of wavelength, then the resistance for current will be more and will be complex (Z):
where X is a reactive part of an antenna radiation resistance. Thus, for each frequency, the radiation will be created by a current flowing over a distance with a length equals to a length of a quarter of a wave length.
Since a triangle with non-equal sides has an asymmetrical shape, its radiation can have a non-horizontal form diagram. To obtain a radiation with a symmetrical shape in a horizontal direction, two not isosceles triangles connected by sides of the same length can be used.
The proposed antenna can have an infinitely wide band, also like a monopole has a minimum active resistance not only when its length is equal to one quarter of a wave. The resistance of the proposed antenna will be minimal and with a length equal to an odd number of quarters of the wave length.
According to a further novel feature of the present invention, a length of a longest one of the lateral sides is not shorter than a quarter of a wave length of a radiation of a desired lower frequency, while a length of a shortest one of the lateral sides is no longer than a quarter of a wavelength of a radiation of a desired highest frequency.
According to a further novel feature of the present invention the electrically conductive plate has a shape of two triangles each formed as a non-rectangular triangle of claim 1 and adjoining each other by their equal sides.
According to a further novel feature of the present invention the two triangles are shortened at their sides opposite to the point connectable to the electrical signal source, and additionally connected at their shortened sides with one another by an electrically conductive strip.
According to a further novel feature of the present invention the electrically conductive plate can have a plurality of through going openings. Transceiver elements operating at frequencies below the radiating frequencies used can be placed in these openings.
The novel features of the present invention are set forth in detail in the appended claims. The invention itself however both as to its construction and its method of operation will be best understood from the following description of the preferred embodiments, which is accompanied by the following drawings.